1. Field of the Invention
The present invention relates to nonwoven fabrics.
2. Related Art
Nonwoven fabrics have been used in a wide variety of fields including sanitary materials such as diapers and sanitary napkins, cleaning products such as cleaning wipers and medical supplies such as masks. Nonwoven fabrics are used in various fields, as described above, and it is necessary for nonwoven fabrics to be produced so as to have characteristics and structures suitable for use in each product application.
Nonwoven fabrics are formed, for example, by forming fiber layers (fiber webs) by using either a dry method or a wet method, and binding the fibers that are included within the fiber layers by chemical or thermal bonding, etc. There are methods in which fiber layers are pierced repeatedly with many needles, or an external physical force is applied to the fiber layers such as water flow injection during the process of binding the fibers, which are included within the fiber layers.
These methods, however, only interlace fibers and do not adjust the orientation or arrangement of fibers in the fiber layers, or adjust the shape of fiber layers. In other words, nonwoven fabrics that are produced according to these methods are just plain sheet-like nonwoven fabrics.
It is said to be desirable for the nonwoven fabrics used as surface sheets of absorbent products, for example, to have irregularities in order to maintain or improve texture when specific liquids such as excretory substance are being absorbed. Nonwoven fabrics with surfaces on which irregularities are formed by forming a number of fiber layers containing fibers of different properties for heat contraction on top of the other to be sealed with heat for inducing heat contraction of specific layers, and the method thereof are disclosed in Japanese Patent No. 3587831.
However, the fiber density of this type of nonwoven fabric increases in a number of heat-sealed areas and the nonwoven fabric may further form into a film because a number of fiber layers are formed on top of the other during formation of irregularities and each fiber layer is heat-sealed and combined. Particularly when the fabric is formed into a film, predefined liquids such as excretory substance have more difficulty in rapidly penetrating the material.